1. Field of the Invention
The present invention relates to a semiconductor device, more particularly, to a quantum semiconductor device employing a plurality of quantum boxes whose degree of freedom of carriers is zero-dimensional.
2. Description of the Related Art
In recent years, advancements in fine semiconductor processing technology and fine structure growing technology have realized the processing of submicron semiconductor regions. In such a fine region, electrons demonstrate quantum mechanical characteristics and their energy levels are quantized. Namely, highly advanced fine semiconductor processing technology is capable of fabricating semiconductor devices on the order of submicrons. In a very fine semiconductor region on the order of a de Broglie wave of an electron in a solid, carriers demonstrate quantum mechanical characteristics, and the energy levels of electrons and positive holes are quantized.
A quantum well layer having the degree of freedom of two dimensions, a quantum thin line (or quantum wire) having a degree of freedom of one dimension, and a quantum box having a degree of freedom of zero dimensions achieve a quantized state that is different from one achieved by three-dimensional particles. Positively utilizing such a quantized state may realize a functional element that provides new functions.
One of the new functions achieved by use of the quantized levels is a resonant tunneling phenomenon. In this resonant tunneling phenomenon, carriers are selectively transferred between adjacent regions by tunneling only when two adjacent energy levels coincide with each other. A resonant hot electron transistor (RHET) with its emitter using the resonance phenomenon has been experimentally fabricated.
Note, quantum semiconductor devices may employ not only two-dimensional regions formed from the quantum well layers explained above but also one- or zero-dimensional regions. For example, Mark A. Reed and Robert T. Bate have proposed quantum semiconductor devices employing a pair of zero-dimensional regions and utilizing an energy resonant phenomenon between the regions (Japanese Unexamined Patent Publication (Kokai) Nos. 61-81662, 61-82470, 61-82471, 61-82472, 61-82473, and 61-123174).